Unstable flow of a magnetically focused unneutralized relativistic electron beam

High-amplitude electron waves with relativistic group velocities were induced on a magnetically focused unneutralized relativistic electron beam. These waves were moving antiparallel to the beam direction and were found to modify drastically the macroscopic beam parameters. The group velocity of these waves depends on the axial magnetic field intensity and on the wave frequency. The importance of this effect to certain applications for relativistic electron beams is discussed